The catalytic preparation of hydrocarbons from synthesis gas, i.e. mixture of carbon monoxide and hydrogen, is well known in the art and is commonly referred to as Fischer-Tropsch synthesis. Catalysts often used for this process comprise one or more metals, together with one or more promoters and a support or carrier material. These catalysts can be made according to one or more well known processes, for instance one or more of precipitation, impregnation, kneading, melting, extrusion and spray drying. Usually these processes are followed by drying, calcination and/or activation.
The products which can be prepared by using these catalysts usually have a very wide range of molecular weight distributions, and in addition to branched and unbranched paraffins, often contain considerable amounts of olefins and oxygen-containing organic compounds, while occasional also aromatic compounds may be formed. Most Fischer-Tropsch reaction result in the formation of longer hydrocarbon chains. Usually only a minor portion of the products obtained is made up of middle distillates, especially when relatively low temperatures are used. Of these middle distillates not only the yield but also the pour point is unsatisfactory. Hydrotreatment (hydrogenation, hydroisomerisation and/or hydrocracking) of the product or part of the product results in a larger amount of desired middle distillates with improved cold flow properties.
Supported catalysts suitable for use in the Fischer-Tropsch synthesis process typically contain a catalytically active metal of the Groups 8, 9 or 10 of the Periodic Table of the Elements. In particular, iron, nickel, cobalt and ruthenium are well known catalytically active metals for such catalysts. Reference may be made to EP-A-398420, EP-A-178008, EP-A-167215, EP-A-168894, EP-A-363537, EP-A-498976 and EP-A-71770. In recent patent publications the emphasis is on cobalt based Fischer Tropsch catalysts for the production of (very) heavy paraffinic product, followed by the hydrocracking of the Fischer Tropsch wax thus obtained to produce middle distillates (in general naphtha, kero and/or gasoil).
There is a continuous interest in finding catalysts which provide a further improved selectivity in the conversion of carbon monoxide into valuable hydrocarbons, in particular hydrocarbons containing 5 or more carbon atoms (“C5+ hydrocarbons” hereinafter), and which minimize the formation of carbon dioxide, which is a carbon containing by-product of low value.
It has now surprisingly been found that cobalt(II)hydroxide can be converted at least partly in the presence of certain transition metals into cobalt(III)oxidehydroxide (CoOOH), which cobalt(III)oxidehydroxide, optionally in combination with unconverted cobalt(II)hydroxide and optionally in the presence of one or more promoters, can be used for the preparation of supported Fischer Tropsch catalysts which show an increased C5+ selectivity.